1. Field of the Invention
The present invention relates to an image forming apparatus in which a toner-image conveyance belt unit can be integrally pulled out from an image forming position to a toner-image conveyance belt replacement position, and more particularly, the present invention relates to a mechanism for manually releasing the tensile force applied to a toner-image conveyance belt after separating a transfer unit from an image bearing member.
2. Description of the Related Art
There is an image forming apparatus in which one or more image bearing members are disposed along a toner-image conveyance belt (such as an intermediate transfer belt or a recording material conveyance belt). In the image forming apparatus including the toner-image conveyance belt, a toner-image conveyance belt unit is supported so that a user can pull out the toner-image conveyance belt unit from a normal image forming position to a toner-image conveyance belt replacement position. The toner-image conveyance belt replacement position includes a toner-image conveyance belt unit replacement position and a maintenance position.
Japanese Patent Application Laid-Open No. 2000-172091 discusses an image forming apparatus in which an intermediate transfer unit supported by a guide rail can be pulled out horizontally along the rotational direction of the intermediate transfer belt. The intermediate transfer unit can be integrally pulled out upwards. When a user pulls out the intermediate transfer unit to replace the intermediate transfer belt, the tensile force applied to the intermediate transfer belt can be changed to release the belt.
Further, Japanese Patent Application Laid-Open No. 2000-187400 discusses an image forming apparatus in which an intermediate transfer unit can be pulled out horizontally along a rotational direction of an intermediate transfer belt. Consequently, the intermediate transfer unit is released from an abutting state against a photosensitive drum.
Further, Japanese Patent Application Laid-Open No. 2000-73035 discusses a tandem-type image forming apparatus in which a plurality of photosensitive drums are arranged along an intermediate transfer belt. An intermediate transfer unit can be pulled out in an axial direction of the photosensitive drum (i.e., in a direction perpendicular to a cross section surface of a rotational direction of the intermediate transfer belt). Further, a transfer roller that press-contacts the photosensitive drum via the intermediate transfer belt forms a transfer portion that can move up and down. The transfer roller is moved down before the intermediate transfer unit is pulled out, so that the intermediate transfer belt does not abrade the photosensitive drum when a user pulls out the intermediate transfer unit.
Further, Japanese Patent Application Laid-Open No. 05-323797 and Japanese Patent Application Laid-Open No. 10-282803 discuss an image forming apparatus that includes an operation lever. The operation lever is used to manually release the tensile force applied to an intermediate transfer belt while separating the intermediate transfer belt from a photosensitive drum. The operation lever is disposed on a side that is parallel to a cross section surface along a rotational direction of the intermediate transfer belt.
However, as illustrated in Japanese Patent Application Laid-Open No. 05-323797 and Japanese Patent Application Laid-Open No. 10-282803, if the tensile force applied to the intermediate transfer belt is released when the intermediate transfer unit is in a normal image forming position, the intermediate transfer belt hangs down. As a result, the intermediate transfer belt may contact a casing member below the intermediate transfer belt. If a user pulls out the intermediate transfer unit from the casing in such a state, the intermediate transfer belt may be stained or folded. In the result, the belt may become unusable.
In order to solve such a problem, an abutting/separating mechanism which abuts and separates the intermediate transfer belt against and from the photosensitive drum and a tensile force releasing mechanism that releases the tensile force applied to the intermediate transfer belt can be independently formed. However, in such a case, a user may operate the wrong operation lever if the operation levers are located adjacent each other.